1. Filed of the Invention
This invention relates to a mold design system for designing, based on a given product shape, a shape of a mold used to manufacture molded articles, and more particularly, to a mold design system for deriving a parting line and an undercut necessary for designing such a mold shape.
2. Description of the Related Art
Process of molding plastics includes injection molding. In injection molding, a fixed quantity of a molten plastic material is injected into an injection mold to mold the plastic into shape. The plastic is thereafter removed from the mold, thus obtaining a product (including a component part etc.). When a plastic product or the like is designed, therefore, it is necessary that a mold for making the product should also be designed at the same time. Present-day product design is in most cases carried out by means of CAD (Computer Aided Design), and accordingly, molds also are designed based on CAD data of products.
A general procedure for designing a mold is as follows:
1) The direction of withdrawing a product is determined, and an undercut is checked.
2) The product is positioned relative to a mold base, and the undercut is dealt with by a slide arrangement or the like.
3) A parting line of the product is set. In this case, outer peripheral edges of the product need to be obtained as the parting line. In cases where the product has a hole therein, peripheral edges of the hole also need to be obtained as a parting line.
4) Based on the parting line thus obtained, a parting face is obtained.
5) The product part is removed from the mold base, which is then divided at the parting face.
FIG. 20 shows parting lines of a product, by way of example. A product model 100 shown in the figure is in the form of a box having a cavity therein. The box opens at its bottom and has a rectangular hole in its top face. When designing a mold base corresponding to this product model 100, a parting line 101 for the outer peripheral portion of the box and a parting line 102 for the hole in the top face are determined. Once the parting lines are determined, parting faces of the mold base can be determined based on the parting lines.
FIG. 21 shows the parting faces of the mold base. The mold base 200 comprises at least two parts 210 and 220 positioned above and below (in Z-axis direction). The upper part 210 is called cavity-side part, and the lower part 220 is called core-side part. A parting face 201 for the outer peripheral portion is determined by the corresponding parting line 101, and a parting face 202 for the hole is determined by the corresponding parting line 102.
Thus, when designing a mold, how to determine the parting line is a matter of importance. In a conventional mold design system, therefore, when an edge which is to constitute the parting line is selected by the designer, edges connected with the selected edge are distinctively shown on screen, thereby assisting the work of deciding the parting line. The designer successively selects suitable edges from among those shown on screen, whereupon the parting line is determined.
FIG. 22 illustrates the method of determining a parting line in the conventional system. In the product model 100, an edge 111 connecting points T3 and T2, for example, is selected, whereupon the edges continuous with point T2 are shown distinctively as selectable edges. In the illustrated example, an edge 112 connecting points T2 and T6 and an edge 113 connecting points T2 and T1 are distinctively shown. When a plurality of edges are shown, which edge is to be selected as the parting line is left to the designer""s judgment.
However, if the product shape is complicated, the parting line is constituted by a large number of edges, and the manual selection of edges consumes much time.
Also, after the parting line is determined, it is necessary to make a check as to whether an undercut exists or not. In a conventional method of determining whether or not an undercut exists, a straight line extending in the withdrawing direction is randomly generated and a portion where the straight line intersects the product twice or more is detected. To increase the detection accuracy, an increased number of straight lines need to be generated, but this requires correspondingly prolonged time.
Thus, the conventional mold design method is associated with a problem that the decision of a parting line consumes much time and labor, imposing a heavy load on the mold designer.
Taking the above into consideration, an object of the present invention is to automate the parting line decision process, thereby improving the efficiency of mold design.
To solve the aforementioned problems, a mold design system for designing a mold for making molded articles is provided which comprises face orientation acquiring means for obtaining orientations of faces constituting a shape of an article to be produced using the mold, face classifying means for classifying the faces into a plurality of sets according to the respective orientations obtained by the face orientation acquiring means, and parting line determining means for determining, as a parting line of the mold for forming the article shape, a boundary between faces that are classified into different sets by the face classifying means.
With this mold design system, the face orientation acquiring means obtains the orientations of faces that constitute the shape of an article to be produced using the mold. Then, according to the orientations of the faces obtained by the face orientation acquiring means, the face classifying means classifies the faces into a plurality of sets. The parting line determining means determines, as the parting line of the mold for forming the article shape, a boundary between faces that are classified into different sets by the face classifying means.